In the field of vehicles, such as automotive vehicles, there have been commonly known a technique for protecting a vehicle occupant by adjusting a pivoting or reclining angle of a seat back (e.g., Japanese Utility Model Laid-Open Publication No. HEI-5-65659).
FIG. 10 hereof schematically shows a conventional vehicle occupant protection apparatus disclosed in the HEI-5-65659 publication, in which section (a) illustrates a general structure of the vehicle occupant protection apparatus, section (b) illustrates the seat back in its reclined position, and section (c) illustrates the seat back in its upright position.
As illustrated in section (a) of FIG. 10, a vehicle seat 100 in the disclosed vehicle occupant protection apparatus 110 comprises a seat cushion or base 101, a seat back 102 and a head rest 103. In the disclosed vehicle occupant protection apparatus 110, a control section 111 controls rotation of four motors 121–124 in accordance with signals received from a seat operation switch 112, vehicle velocity sensor 113 and position sensor 114. The first motor 121 drives a slide mechanism 125 to slide the seat base 101 horizontally in a front-and-rear direction of the vehicle. The second motor 122 drives a front height mechanism 126 to pivot a front portion of the seat base 101 vertically in a top-and-bottom direction of the vehicle. The third motor 123 drives a rear height mechanism 127 to pivot a rear portion of the seat base 101 vertically in the top-and-bottom direction of the vehicle. The fourth motor 124 drives a reclining mechanism 128 to pivot the seat back 102 vertically in the front-and-rear direction of the vehicle.
As illustrated in section (b) of FIG. 10, the control section 111 generates a signal to the fourth motor 124 once the vehicle velocity detected by the velocity sensor 113 exceeds a predetermined velocity value while the pivoting (i.e., reclining) angle θr of the seat back 102 is greater than a predetermined reference angle θs. As a consequence, the seat back 104 can be pivoted compulsorily up to the reference angle θs. The “reclining angle θr” means an inclination angle through which the seat back 102 is inclined relative to the vertical line. In the illustrated example, the predetermined reference angle θs is 25°.
In ordinary use of the vehicle seat 100, the seat back 102 is often kept inclined rearwardly approximately to the reference angle θs (i.e., the reclining angle θr is kept approximately equal to the reference angle θs), as seen in section (c) of FIG. 10, in order to give sitting comfort to the vehicle occupant Mn seated in the seat 100. In the event a rear-end collision has occurred to the vehicle in such use condition of the vehicle seat 100, the upper half of the body of the vehicle occupant Mn would be forced rearwardly due to inertia of the vehicle occupant Mn, namely, due to reactive force of the read-end collision. Because the seat back 102 is kept in the rearwardly-inclined position, there would occur so-called “floating-up” of the occupant's body, i.e. the body of the vehicle occupant Mn is thrown upwardly and rearwardly along the inclined seat back 102 due to an upward component of the inertia.